This invention relates in general to vehicle wheels and particular to cast vehicle wheels having a pilot hole communicating with a milled drain slot.
In the past, vehicle wheels typically have been formed entirely from steel. However, wheels formed from light weight metals, such as aluminum, magnesium and titanium, or alloys thereof, have become increasingly popular. In addition to weighing less than conventional all-steel wheels, such light weight wheels can be manufactured having a pleasing esthetic shape. Weight savings also can be achieved by attaching a wheel disc formed from a light weight metal alloy to a steel wheel rim.
Referring now to the drawings, FIG. 1 illustrates a typical one piece vehicle wheel 10. The vehicle wheel 10 can be cast or forged from an aluminum alloy to produce a wheel casting or forging having physical dimensions that are close to the desired final wheel dimensions. The casting is then machined to the desired final dimensions. The vehicle wheel 10 includes an annular wheel rim 12 and a circular wheel disc 14. The wheel disc 14 can be formed across the outboard end of the wheel rim 12, as shown in FIG. 1, or recessed within the wheel rim.
The wheel rim 12 is adapted to carry a pneumatically inflated tire and has outboard and inboard tire retaining flanges 16 and 18, respectively, formed on the ends thereof that extend in an outward radial direction to retain the tire upon the wheel. Outboard and inboard tire bead seats 20 and 22, respectively, are formed on the outer surface of the wheel rim 12 adjacent to the corresponding tire retaining flange to support the tire wall beads (not shown) and form an air-tight seal therewith. The wheel rim 12 also includes a reduced diameter deep well 24 between the tire bead seats 20 and 22 to facilitate mounting the tire upon the wheel.
The wheel disc 14 includes a central wheel hub 30 for mounting the wheel 10 upon a vehicle. The inboard face 32 of the wheel disc hub is typically machined to form a flat surface to assure good contact between the wheel disc and a vehicle axle hub. A pilot hole 34 and a plurality of wheel stud holes 36 extend through the wheel hub 30. The pilot hole 34 is centered upon the hub 30 while the wheel stud holes 36 are spaced equally about a bolt hole circle that is concentric with the pilot hole 34. The pilot hole 34 can receive the end of an axle while the wheel stud holes 36 receive wheel studs (not shown) for attaching the wheel 10 to the vehicle. As shown in FIG. 1, a plurality of lightener pockets 38 extend axially into the inboard face 32 of the wheel hub 30. The lightener pockets 38 further reduce the weight of wheel and are spaced between the wheel stud holes 36. The wheel disc 14 also typically includes a plurality of wheel spokes 40 which extend radially from the wheel hub 30 to the wheel rim 14 and support the hub within the rim.
A pilot hole cover 42 extends over the outboard end of the wheel hub 30. As shown in FIG. 2, a plurality of tabs 44 (two shown) extend into the pilot hole 34. A barb 46 formed upon the end of each tab 46 cooperates with a flange 47 formed upon the pilot hole wall to frictionally secure the cover 42 to the wheel hub 30. Such covers 42 are typically formed from plastic and provide a pleasing esthetic appearance for the wheel hub center. While the cover 42 shown in the figures is recessed into the outboard end of the pilot hole 34, covers may also rest against the outboard surface of the wheel hub 30 (not shown). While either type of cover appears to be fit closely with the wheel hub and pilot hole 34, the covers do not actually form a seal with the wheel hub surface. Accordingly, water has been known to seep between the cover 42 and the wheel hub surface and enter the pilot hole 34 when the vehicle is driven through a car wash or puddles. When the water contacts a steel grease cap that extends from the axle hub into the pilot hole, galvanic action may result. If the galvanic action occurs over a period of time, the resulting corrosion may make removal of the wheel from the vehicle difficult. Additionally, during cornering maneuvers of the vehicle, rusty water may be forced from the pilot hole, staining the outboard wheel face.
As best seen in FIG. 2, it is known to form a radially extending drain slot 48 in the inboard surface of the wheel hub 32 of the wheel hub 30. As illustrated in FIG. 2, the drain slot 48 includes a inner drain slot 50, which is typically about 16 mm deep, extending from the pilot hole 34 to the lightener pocket 38, and an outer drain slot 52 extending from the lightener pocket 38 to the edge of the wheel hub 30. As the vehicle is driven, centrifugal forces urge any water present within the pilot hole 34 through the drain slot 48 and out of the center of the wheel hub 30.
It is known to form pilot hole drain slots 48 by casting or machining. With the casting method, the wheel mold is modified to include a pair of drain slot cores to form the inner and outer drain slots 50 and 52, respectively. However, the provision of a drain slot core for forming the inner drain slot 50 requires a reduction in diameter of the mold riser positioned over the center of the wheel hub, which, in turn, reduces the amount of molten metal available to compensate for shrinkage as the wheel casting cools. The inventors have found that the wheel reject rate increases to an unacceptable level when the inner drain slot 50 is cast into the wheel disc hub. Alternately, the inner drain slot 50 may be milled into the inboard surface of the wheel hub. However, milling requires a substantial amount of machining time, especially if multiple drain slots are provided. The additional machining time and the associated wear on the milling cutters increases manufacturing costs. Accordingly, a different drain slot that would reduce reject rates and/or manufacturing costs would be desirable.